This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. Our goal for this project is to design and synthesize novel peptide and peptido-mimetic inhibitors, specifically targeted against proteases central to the pathogenesis of malaria, schistosomiasis, trypanosomiasis, and hepatitis A. Crystal structures and in some cases homology-based structural models for target proteases are used for computer-graphics based modeling of ligand binding, for database screening of potential inhibitors as well as for analysis of potential binding modes. Optimization of these compounds is aimed at improving specificity, half-life, and diminishing toxicity. Using medicinal chemistry approaches, we have designed and synthesized a wide variety of chemical compounds which include heteroaromatic inhibitors, peptide-based and peptidomimetic inhibitors. In the early years of this project, mass spectrometry has played an important role in chemical characterization of these lead compounds. Proteomic analysis is also important at early stages of target identification, using affinity based probes that target specific functional subclasses of protease activities.